It is known practice to produce acrylic esters by carrying out an esterification reaction between an alcohol and acrylic acid. This reaction is an equilibrated catalyzed reaction with generation of water:CH2═CH—COOH+R—OHCH2═CH—COOR+H2O
It is necessary to remove the water produced during the reaction in order to shift the equilibrium in the direction of the production of the acrylic ester.
This reaction is generally accompanied by side reactions which produce impurities that it is necessary to remove with a view to obtaining the acrylic ester with a high purity which meets the technical requirements associated with its final use as a monomer for manufacturing polymers that can be used in numerous fields of application.
Moreover, for obvious economic reasons, the exploitable products present in the crude reaction mixture, in particular the unreacted reagents and the catalyst, are as far as possible recycled within the process.
To these ends, a separation/purification process comprising a set of distillations, extractions and/or separations by settling out, which is both relatively complex to carry out, in particular due to the presence of azeotropic mixtures, and costly in terms of energy, is generally carried out.
Document U.S. Pat. No. 6,072,076 describes a process for producing alkyl(meth)acrylates by esterification of (meth)acrylic acid with an alcohol which has a chain length ranging from 1 to 8 carbon atoms, in the presence of an acid catalyst. In this process, the equilibrium of the reaction is shifted by removal of a mixture comprising water and alcohol in a rectification unit III at the top of the reaction zone. The aqueous mixture, after condensation, is treated in a separator 17 in order to purify the alcohol and recycle it to the reaction by means of the rectification column III, the separated aqueous phase being partially returned to the rectification unit III.
In this process, the reaction mixture resulting from the reaction zone is sent to a rectification unit I in which the mixture is separated into a product (I) comprising the desired ester, the residual alcohol and the residual acid, and a product (II) comprising the catalyst; the product (I) is subjected to a second rectification unit II in which the desired ester is separated from the residual alcohol and acid products, which are recycled to the reaction zone, the purified ester being taken off at the side.
This process is illustrated with the manufacture of 2-ethylhexyl acrylate from the alcohol 2-ethylhexanol, carried out by means of two reactors 5 and 6 placed in series and operating at different heat levels. The rectification column III, the liquid reflux 13 of which contains partially recycled water, surmounts the first reactor. A crude reaction mixture containing 70% of 2-ethylhexyl acrylate is derived from this first reactor 5. The reaction is continued in the second reactor 6 with continuous take-off of the water produced by the reaction using the rectification unit III so as to achieve a final 2-ethylhexyl acrylate content of 82%.
In the process described in document U.S. Pat. No. 6,072,076, because of the introduction of recycled water into the rectification column, the removal of the water generated by the reaction is not complete for shifting the equilibrium of the reaction. It therefore proves to be necessary to use a second reactor in order to achieve satisfactory yields.
The process described in document U.S. Pat. No. 6,072,076 is not applicable to the manufacture of 2-octyl acrylate via an esterification reaction of acrylic acid and of 2-octanol. This is because 2-octanol is a secondary alcohol which is much more sensitive than a primary alcohol, such as 2-ethylhexanol, to a dehydration reaction in the presence of acid catalyst, leading to the formation of octenes and of water. There is a risk that this formation of water, accumulated with the reintroduction into the system of at least one part of the aqueous phase generated by the esterification reaction, will more readily retrograde the desired 2-octyl acrylate to 2-octanol and acrylic acid by hydrolysis. Moreover, according to said document, the purification of the crude reaction mixture comprising the desired acrylate and residual alcohol is carried out by distillation in the rectification unit I with a long residence time in the presence of the acid catalyst. In the case of a synthesis with 2-octanol, there is also a risk that this distillation will generate octenes and water and will at least partially degrade the 2-octyle acrylate formed.
The Applicant Company has sought to solve these various problems associated with the use of 2-octanol in the esterification reaction with acrylic acid.
In document US 2008/0087196, the synthesis of 2-octyl acrylate according to an esterification reaction with 2-octanol, in the presence of p-toluenesulfonic acid, is described. The reaction is carried out in a solvent medium in order to remove the water produced in the form of a toluene/water azeotrope. Such a process is nevertheless complicated to implement on an industrial scale.
Moreover, documents EP 1 027 322 and EP 1 028 936 describe a process for removing the sulfur originating from the use of a sulfonic acid catalyst, in a process for the production of acrylate, in particular of butyl acrylate, of 2-ethylhexyl acrylate or of polyol acrylate. However, the application of such a process for the synthesis of 2-octyl acrylate is in no way suggested.
There still remains therefore a need to have a process for manufacturing 2-octyl acrylate which has a productivity compatible with industrial-scale manufacture and which results in a 2-octyl acrylate which meets the purity requirements associated with its final use.
The objective of the present invention is the manufacture of a 2-octyl acrylate of very high purity with a high yield with the use of a single reactor, and including the recycling of the exploitable products such as, on the one hand, the unreacted reagents and, on the other hand, the acid catalyst, in particular an acid catalyst comprising sulfur, in particular of the sulfonic acid type.
The solution proposed consists in not directly reintroducing the aqueous phase produced by the reaction into the rectification column in order to optimize the shift in equilibrium of the reaction in the direction of the production of the ester, and in separating the acid catalyst with a view to the recycling thereof prior to the whole of the process for purifying the desired 2-octyl acrylate.
According to the invention, the catalyst, in particular acid catalyst comprising sulfur, is reused in the reaction process. The emission of organosulfur compounds during the process for producing 2-octyl acrylate using a catalyst of sulfonic acid type is thus reduced, making the process according to the invention environmentally friendly.
The present invention also makes it possible to produce an acrylic ester comprising carbon of renewable origin associated with the use of 2-octanol, which is an alcohol derived from vegetable matter.